Search Results (85)

Porcine reproductive and respiratory syndrome virus (PRRSV) infection causes significant economic losses in swine production. In May 2021 and March 2023, we detected PRRSV genes in serum samples from two weaned pigs with respiratory disorders on a farm in Japan. Partial gene sequences of these strains closely resembled those of a PRRS vaccine strain. We subsequently isolated two PRRSV field strains, KU-IG21-1 and KU-IG23-1, from the 2021 and 2023 samples, respectively. The KU-IG21-1 strain exhibited more pronounced cytopathic effects and significantly higher replication efficiency in cultured cells compared to both the vaccine and KU-IG23-1 strains. Despite these phenotypic differences, complete genome sequencing revealed high genetic similarity between the field isolates and the vaccine strain, with only 16 and 24 amino acid differences in the KU-IG21-1 and KU-IG23-1 strains, respectively. These findings suggest that the field strains likely emerged through the accumulation of point mutations in the vaccine strain rather than through homologous recombination. Furthermore, we identified three amino acid substitutions that may contribute to the enhanced replication of the KU-IG21-1 strain. This study underscores the potential impact of point mutations on PRRSV phenotypes and provides new insights into the complex evolutionary dynamics of PRRSV. Full article

Background: Porcine reproductive and respiratory syndrome virus (PRRSV) causes significant economic losses for the global swine industry. Gilt immunization using modified live virus (MLV) vaccines is crucial for herd stability, but it is complicated by frequent mixed infections of PRRSV strains on farm. This study monitored the administration of tylvalosin during a PRRSV-2 MLV (TJM) immunization program, focusing on viral dynamics and immune responses in gilts naturally exposed to co-circulating classical (GD240101) and highly pathogenic like (HP-PRRSV-like, GD240102) PRRSV strains. Methods: The animal study was approved by the Laboratory Animal Ethical Committee of China Agricultural University. One hundred gilts were randomized into control and tylvalosin groups (n = 50/group). All received the TJM MLV vaccination. The tylvalosin group received tylvalosin tartrate premix cyclically in-feed for three cycles. Serum and saliva samples were collected periodically. PRRSV RNA (RT-qPCR) and specific antibodies (ELISA) were assessed. Viral population dynamics (relative abundance, mutation, recombination of TJM, GD240101, and GD240102) were monitored via next-generation sequencing (NGS) on a pooled PRRSV-positive sample. Results: In this field trial where tylvalosin was used, a shorter duration of PRRSV viremia and saliva shedding was observed to compare with controls. NGS analysis showed accelerated vaccine strain (TJM) clearance in the tylvalosin group (by week 3 vs. week 9 in control). Field strain dynamics were also altered, showing a faster decline in the tylvalosin group. Antibody response uniformity was altered, with lower coefficient of variation (CV) for PRRSV and CSFV observed following tylvalosin usage. Conclusions: In gilts receiving tylvalosin for the management of bacterial pathogens during a PRRSV MLV immunization program, it was associated with accelerated viral clearance and enhanced systemic immune response uniformity under mixed-infection field conditions. NGS provides invaluable data for dissecting these complex viral dynamics. Crucially, these findings describe a biological drug–host–virus interaction and should not be interpreted as an endorsement for the prophylactic use of antimicrobials. In alignment with global antimicrobial stewardship principles, tylvalosin should be reserved for the therapeutic treatment of diagnosed bacterial diseases to mitigate the risk of promoting resistance. Full article

Porcine reproductive and respiratory syndrome virus (PRRSV), a major pathogen causing substantial economic losses in the global swine industry, was studied in southern Xinjiang to characterize its local epidemic features. Based on 632 clinical samples collected from 13 pig farms between 2023 and 2025, quantitative RT-PCR detection showed an overall positivity rate of 18.35% (116/632), with PRRSV-2 single infection accounting for 97.41% (113/116), PRRSV-1 single infection for 1.72% (2/116), and co-infection for 0.86% (1/116). Among 38 ORF5 sequences obtained from positive samples, Sublineage 1.8 (NADC30-like) was dominant, comprising 97.14% of successfully sequenced strains. Molecular analysis revealed that PRRSV-1 isolates carried six amino acid mutations including A129V (consistent with the Chinese strain CN/FJFQ-1/2023), while PRRSV-2 strains exhibited key variations such as the neutralization escape mutation Q13R, virulence-associated site K151R, and an anomalous vaccine marker A137. Furthermore, a recombinant strain (XJLETUQ2025-7) between NADC30 and VR-2332 was identified with breakpoints in NSP2 and NSP10. Serological surveillance of 2043 vaccinated pigs showed an overall antibody positive rate of 83.0% (1696/2043), with increasing annual rates from 72.3% (2023) and 75.4% (2024) to 91.3% (2025). In conclusion, the PRRSV epidemic in southern Xinjiang is primarily driven by NADC30-like strains of PRRSV-2, with recombination events and GP5 epitope variations posing challenges to disease control. These findings enhance the epidemiological understanding of PRRSV in the region and provide valuable insights for vaccine development and prevention strategies. Full article

Porcine reproductive and respiratory syndrome virus remains one of the most economically significant pathogens in swine production, with PRRSV-2 being the dominant variant in the United States. While lineage classification has traditionally relied on ORF5 sequencing, recent studies suggest that this single-gene approach may overlook key evolutionary events such as recombination. In this study, we performed whole-genome sequencing and phylogenetic analysis of seven PRRSV-2 isolates collected in the U.S. between 2006 and 2024. Using reference-guided assembly, lineage assignment, and recombination detection with RDP5 and SIMplot, we identified discordant phylogenetic placements between ORF5 and whole genomes in four of the seven isolates. These discordances were explained by multiple recombination events affecting different genomic regions, particularly ORF2–ORF7. In contrast, three isolates showed phylogenetic concordance and no strong evidence of recombination. Our findings demonstrate that recombination plays a significant role in shaping PRRSV-2 evolution and highlight the limitations of ORF5-based lineage classification. Whole-genome surveillance is therefore essential to accurately track viral diversity, detect recombinant strains, and inform control strategies. This work underscores the need for a broader adoption of full-genome analysis in routine PRRSV surveillance and research. Full article

PRRSV continues to evolve, complicating its epidemiological landscape in China. In this study, we isolated a novel PRRSV strain, GZ2022, from a swine farm in Guizhou Province. Subsequent analyses performed on this isolate included complete genome sequencing, phylogenetic analysis, recombination assessment, and characterization of its biological properties. Phylogenetic analysis revealed that GZ2022 clusters within Lineage 1 (NADC30-like) and features a 131-amino-acid deletion in NSP2, consistent with NADC30-derived strains. Recombination analysis identified NADC30 as the major parental strain (75% genomic contribution), with a minor recombinant region (25%) derived from the highly pathogenic HuN4 strain. In vitro growth kinetics revealed peak viral titers in Marc-145 cells at 72 h post infection (hpi). Pathogenicity was evaluated in 21-day-old piglets infected with GZ2022, the highly pathogenic PRRSV strain WUH3, or negative controls. Both infected groups exhibited typical PRRS clinical signs (fever, respiratory distress) and histopathological lesions (interstitial pneumonia, pulmonary consolidation). However, GZ2022-infected piglets exhibited attenuated virulence compared to WUH3, with reduced pulmonary hemorrhage and 0% mortality compared to 80% in the WUH3 group. Seroconversion (N-protein antibodies) was observed at 14 dpi (days post inoculation) in GZ2022-infected animals, persisting throughout the 28-day trial. Viral shedding dynamics aligned with moderate pathogenicity. These findings classify GZ2022 as a moderately virulent NADC30-like recombinant strain with partial HuN4-derived genomic regions. The emergence of such strains underscores the need for sustained surveillance of PRRSV genetic diversity and systematic evaluation of the biological properties of novel variants to refine control measures and inform vaccine development. Full article

Porcine Reproductive and Respiratory Syndrome Virus 2 (PRRSV-2) represents one of the greatest threats to global pork production. Increased incidence of a genetic variant of Porcine Reproductive and Respiratory Syndrome Virus (variant 1H.18) was recently reported in the Midwestern USA Sequence comparisons in the ORF5 region indicate that 1H.18 was closely related to both sub-lineages L1H and L1C. To expand our understanding and attempt to elucidate the origin of the 1H.18, we sequenced a near-complete genome, covering all coding regions, and investigated the occurrence of recombination events that may have contributed to the emergence of the new variant. At least six distinct recombination events were identified across the coding portion of the genome. Evidence of recombination in the ORF5 region between variants 1H.31 and 1C.3 was detected. Our results suggest a likely origin of 1H.18 driven by recombination. Full article

Background: Porcine Reproductive and Respiratory Syndrome (PRRS) is a highly contagious disease characterized by reproductive failure in sows and severe respiratory disorders across all swine ages, causing significant economic losses. In China, the PRRSV epidemiological landscape is complex, with the coexistence of multiple lineages and frequent recombination. The major circulating strains include sublineages 1.8 (NADC30-like PRRSV) and 1.5 (NADC34-like PRRSV), along with lineages 8 (HP-like PRRSV) and 5 (VR2332-like PRRSV), highlighting the urgent need for rapid detection and lineage differentiation. Methods: A quadruplex RT-qPCR assay was developed targeting lineage-specific deletions in the NSP2 gene to simultaneously detect PRRSV-2 and differentiate NADC30-like PRRSV, HP-like PRRSV, and NADC34-like PRRSV strains. The assay was optimized with respect to reaction conditions, including annealing temperature, primers, and probe concentrations. The method’s performance was evaluated in terms of specificity, sensitivity, repeatability, stability, limit of detection (LOD), and consistency with sequencing results. Results: The assay demonstrated high sensitivity (LOD of 3 copies/μL), high specificity, and good repeatability (coefficient of variation < 1.5%). Field application using 938 samples from Guangxi A and B farms revealed NADC30-like PRRSV wild-type strains at positivity rates of 13.44% and 3.53%, respectively. Positive samples selected for sequencing were further confirmed using ORF5-based phylogenetic analysis and NSP2 deletion pattern comparison, which aligned with RT-qPCR detection results. Field application primarily detected NADC30-like PRRSV, while further validation is still needed for HP-like and NADC34-like strains. The developed quadruplex RT-qPCR assay enables rapid and simultaneous detection of PRRSV-2 and differentiation of three major lineages, providing a sensitive, specific, and reliable tool for distinguishing vaccine-derived from circulating strains and supporting targeted disease surveillance and control in swine farms. Full article

Porcine reproductive and respiratory syndrome virus (PRRSV) is a major viral threat to swine, causing significant economic loss in the global pig farming industry. This virus includes two major genotypes, PRRSV1 and PRRSV2, both characterized by high mutation rates and genetic variability, complicating the development of a universally effective vaccine and disease control. To address this challenge, this study utilizes immunoinformatics tools to identify conserved epitopes and design a multi-epitope vaccine candidate against PRRSV based on reverse vaccinology. The complete sequences of PRRSV-encoded proteins were retrieved worldwide, and the conserved fragments were identified through the alignment of polypeptide sequences. Subsequent screening was conducted to screen epitopes for their potential to be safe and to activate B cells, HTLs (helper T cells), and CTLs (cytotoxic T cells). By conjugating the selected epitopes with distinct adjuvant proteins, three vaccine candidates were designed and termed PRRSV-vaccine (PRRSV-V-1, PRRSV-V-2, and PRRSV-V-3, respectively). Furthermore, systematic evaluations of their physicochemical properties, structural stability, binding with pattern recognition receptors, and induction of the host immune system were performed. PRRSV-V-2 had the most promising physicochemical and structural characteristics, strong binding with toll-like receptors (TLR3 and TLR8), and the most vigorous reactions to host immune responses. As the most promising candidate, the recombinant PRRSV plasmid was in silico designed for expression in Escherichia coli. Our study proposed a novel approach to PRRSV vaccine development against PRRSV, offering a promising strategy for controlling the infection across diverse PRRSV strains in swine. Despite providing significant insights into vaccine design through computational methods, the results of this study remain predictive. So, it is open for the experimental validations of the scientific community to ensure its actual immunological properties, especially the safety and efficacy. Full article

Due to its high genomic variability, the epidemiological landscape of porcine reproductive and respiratory syndrome virus (PRRSV) has become increasingly complex in recent years. From 2022 to 2023, we collected a total of 1044 clinical samples from pigs suspected of PRRSV infection in China and discovered a PRRSV-positive rate of 29.8% (311/1044) using RT-PCR targeting the nsp2 gene. Among these positive samples, NADC30/34-like PRRSV, highly pathogenic PRRSV (HP-PRRSV), and classical PRRSV strains accounted for 60.1%, 37.9%, and 4.5%, respectively. These results indicate that the most prevalent PRRSV strains in China are NADC30/34-like PRRSV, followed by HP-PRRSV. Two PRRSV strains, JX03 and HN08, were isolated, and TCID₅₀ assays were performed to determine their titers at different time points post-infection, revealing differences in their proliferation kinetics. Phylogenetic, amino acid sequence, and recombination analyses demonstrated that the JX03 and HN08 strains cluster within lineage 8 (HP-PRRSV) and sublineage 1.5 (NADC34-like PRRSV), respectively. Notably, the HN08 strain was identified as a recombinant between the NADC30-like and NADC34-like strains, while no recombination event was detected in the JX03 strain. Pathogenicity assessments showed that the JX03 strain exhibited higher pathogenicity than the CHN-HB-2018 strain (a NADC30-like PRRSV strain was previously isolated by our lab), as evidenced by differences in clinical signs and mortality rates in piglets. In contrast, HN08 displayed no obvious clinical symptoms or mortality, revealing lower pathogenicity than the CHN-HB-2018 strain. These findings provide valuable information on the epidemiological and genetic characteristics of PRRSV strains in China, laying a foundation for the development of effective strategies against PRRSV. Full article

First reported in 1987, the porcine reproductive and respiratory syndrome virus (PRRSV) has significantly disrupted the major regions affected by PRRSV in the pig breeding industry. Recently, outbreaks of disease caused by recombinant PRRSV strains in China have raised serious concerns. Effective immunization and infection control in pig populations is critical, as the virus frequently undergoes mutation and recombination. This study characterized a novel recombinant PRRSV strain, BX/CH/22, isolated from Northeast China. Genetic analysis revealed that BX/CH/22 is a recombinant of JXA1, NADC 30-like, and NADC 34-like strains. Phylogenetic analysis of the non-structural protein (NSP) 2 region classified BX/CH/22 as JXA1 PRRSV-like, with a characteristic deletion of 30 discontinuous amino acids in NSP2. However, Open Reading Frame (ORF) 5 analysis classified it as NADC 30-like PPRSV, while whole-genome phylogenetic analysis classified it as NADC 34-like PPRSV. Recombination analysis revealed that BX/CH/22 contains an NADC 34-like PRRSV backbone, an NSP-coding region from NADC 30-like PRRSV, and an ORF2-ORF6 region from NADC 34-like PRRSV. The strain was isolated from serum samples obtained from commercial swine farms undergoing active PRRS outbreaks. In animal experiments, all BX/CH/22-challenged piglets exhibited persistent fever, with peak temperatures >40.5 °C at 4–9 dpi resolving by 11 dpi, accompanied by cough, anorexia, and lethargy. A significant reduction in daily weight gain was observed in infected groups compared to asymptomatic controls, with a 100% survival rate. Our findings provide early warning for PRRSV immune control strategies. Full article

Porcine reproductive and respiratory syndrome virus (PRRSV) is considered a promising viral vector for the expression and delivery of foreign genes for the development of a new generation of multi-valent vaccines against PRRSV and other porcine viruses, as well as for analyses of the immune response against PRRSV and anti-PRRSV component screening. In the present study, the junction site between nsp1β and nsp2 in the PRRSV genome was tested for the insertion and expression of foreign genes. Three foreign genes, including eGFP, iLOV3, and TEVp, were inserted into the intergenic junction between nsp1β and nsp2 and expressed by the respective recombinant PRRSVs (rPRRSV-SH01-eGFP, rPRRSV-SH01-iLOV3, and rPRRSV-SH01-TEVp) in vitro in mammalian cells. Analysis of the growth kinetics of the rescued recombinant PRRSVs showed no significant differences between the recombinant PRRSVs and their parental viruses. The inserted genes were consistently present in the viral genome during serial passage in vitro (for at least 20 passages). In addition, rPRRSV-SH01-eGFP can be used as a reporter virus for rapid detection of neutralizing antibodies against PRRSV through a fluorescent focus unit reduction-based assay. These data demonstrate that the junction between nsp1β and nsp2 is a new site that is suitable for the insertion and expression of foreign genes, providing a new option to express and deliver foreign genes using PRRSV-based vectors for different purposes, such as the development of multi-valent vaccines against PRRSV and other porcine viruses. Full article

Background: Porcine reproductive and respiratory syndrome (PRRS) has been present in China for about 30 years, and because of the high mutability of PRRSV, it causes huge economic losses to pig enterprises every year. PRRSV-2 is widely prevalent in China, and the detection rate of PRRSV-1 is also on the rise. Nonstructural protein 2 (NSP2) is a highly variable protein with multiple biological functions, such as PRRSV replication, which plays an important role in understanding PRRSV variation and epidemic alerts. Objectives: The epidemic characteristics and recombination of PRRSV-1 NSP2 are still unknown. The purpose of this study is to study the epidemic characteristics of PRRSV-1 NSP2 and lay a foundation for the prevention and control of PRRSV-1. Methods: In this study, we collected several PRRSV-1 and PRRSV-2 NSP2 gene sequences for gene sequence and recombination analyses, aiming to analyze the recombination pattern and genetic variation in the PRRSV-1 NSP2 genes in China. Results: The genetic similarity results showed that the 69 PRRSV-1 NSP2 gene sequences collected in this study showed nucleotide similarity ranging from 67.3% to 100.0% and amino acid similarity ranging from 64.3% to 100.0%. Amino acid sequence comparison showed that PRRSV-1 had more amino acid deletion or substitution sites than PRRSV-2. NSP2 also contains special amino acid regions such as the highly immunogenic region. PRRSV-1 can be categorized into four strains, NMEU09-1-like, BJEU06-1-like, HKEU-16-like and Amervac-like isolates, and are at different positions in the ML and NJ phylogenetic trees. In the ninety selected PRRSVs, six recombination events were detected using recombination analysis, two of which occurred in Chinese PRRSV-1 strains. Therefore, sequence analysis of NSP2 helps us to understand the prevalence and variation in PRRSV-1 in China over the past two decades and provides a theoretical basis for studying the epidemiology and evolution of NSP2. Full article

Porcine reproductive and respiratory syndrome virus (PRRSV) continues to be a major threat to the global swine industry, causing significant economic losses. To address this, we developed a scalable recombinant adeno-associated virus (rAAV)-based strategy for the delivery of soluble viral receptors (SVRs) to treat and potentially eliminate PRRSV infections. This strategy involves fusing the virus-binding domains of two key cellular receptors, sialoadhesin (Sn4D) and CD163 (SRCR5-9), with an Fc fragment. We then used an insect cell–baculovirus expression vector system to produce the rAAV-SRCR59-Fc/Sn4D-Fc vector. Through a series of optimizations, we determined the best conditions for rAAV production, including a baculovirus co-infection ratio of 0.5:1.0, an initial insect cell density of 2.0 × 10⁶ cells/mL, a fetal bovine serum concentration of 2%, and a culture temperature of 30 °C. Under these optimized conditions, we achieved a high titer of rAAV-SRCR59-Fc/Sn4D-Fc in a 2 L bioreactor, reaching 5.4 ± 0.9 × 10⁹ infectious viral particles (IVPs)/mL. Notably, in vitro neutralization assays using a Transwell co-culture system demonstrated a 4.3 log reduction in viral titers across genetically diverse PRRSV-2 strains, including VR2332, JXA1, JS07, and SH1705. Collectively, this study provides a robust platform for large-scale rAAV production and highlights the potential of SVR-based gene therapy to address the antigenic diversity of PRRSV-2. Full article

Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) is one of the most significant infectious agents threatening the global pig industry. Due to its high mutation and recombination rates, the prevalence of PRRSV in domestic pig populations is complex. To better understand the epidemiology of PRRSV, we conducted a large-scale investigation in eastern China, focusing on pig farms with a history of high abortion rates. A total of 14,934 pig samples were collected from 11 sow farms and 53 fattening farms across three provinces. Among these, 13.0% of the collected samples tested positive for PRRSV, with specific prevalence rates of 19.7% in sows and 12.4% in piglets. Genetic evolution analysis of the GP5 gene from 43 PRRSV strains identified in this study revealed that NADC30-like, NADC34-like, and HP-PRRSV were the predominant lineages in domestic pig farms. The NADC30-like genotype was the most dominant and had evolved into three subgenotypes, while the NADC34-like strains had diverged into two subgenotypes. Further analysis of the Nsp2 gene from 18 strains indicated that the NSP2 gene of multiple NADC34-like strains was closely related to that of the NADC30-like, suggesting that the NADC34-like strains are primarily recombinant viruses. Sequence comparison of the Nsp2 gene showed that both NADC30-like and NADC34-like viruses share 111 amino acid deletions at positions 322–433 and 21 amino acid deletions at positions 539–558 in the Nsp2 gene coding region. For the first time, the pathogenicity of a representative NADC34-like virus isolated in China was evaluated in pregnant sow. The results showed that infected sows exhibited an increased body temperature, ear cyanosis, and typical edema and cyanosis of the external genitalia. Moreover, all infected sows experienced miscarriage, with 100% of the aborted piglets being stillbirths exhibiting a high virus load. These findings indicate that this NADC34-like virus is highly virulent to sows. Full article

NADC34-like porcine reproductive and respiratory syndrome virus (PRRSV) has been circulating in China for several years, causing substantial economic losses to the local pig industry. Current commercial vaccines have failed to provide complete protection against NADC34-like PRRSV infection. Additionally, the poor adaptation of NADC34-like strains to Marc-145 cells presents a considerable challenge for developing effective vaccines against these strains. This study addresses these challenges by developing a novel vaccine candidate against NADC34-like PRRSV. We engineered a recombinant PRRSV, rNADC34-CHSps, by replacing the structural protein region of the JS2021NADC34 strain with that of the CHR6 strain to improve its adaptation to Marc-145 cells. The rescued strain could proliferate well in Marc-145 cells, maintaining high titers and stable growth kinetics even at high passage numbers. Piglets were vaccinated with rNADC34-CHSps at passage 80 and then challenged with the virulent NADC34-like PRRSV strain, JS2021NADC34, at 28 days post-vaccination. All vaccinated piglets developed specific antibodies against PRRSV at 14 dpv and showed no significant clinical symptoms, even after exposure to PRRSV JS2021NADC34. Furthermore, the vaccinated piglets gained significantly more weight, displayed much less severe pathological lesions, and reduced viremia compared to the challenge control piglets. These results indicate that rNADC34-CHSps is a promising vaccine candidate against NADC34-like PRRSV infection, highlighting the potential of targeted genomic modifications to enhance vaccine efficacy. Full article